Helicopter type aircraft are known to be aerodynamically unstable. The piloting process for such vehicles involves the active use of both hands and both feet, as well as close attention to the aircraft attitude. The process is especially complicated due to the interrelated nature of the controls. An increase in the pitch of the main rotor causes a twisting of the aircraft which must be corrected for by an adjustment of the tail rotor. In a similar manner, when the pilot desires to perform a single action with the aircraft, he must simultaneously perform a complex, learned series of actions on the controls in order to achieve the single action.
In addition, helicopter type aircraft typically are able to operate closer to the limit of their material strength and limit of their flight envelope. An overstressing of the aircraft can cause mechanical damage. An over specification of a number of flight characteristics can also push the aircraft beyond its limit, or cause none of the characteristics specified to be achieved.
Although there are numerous examples of advancement of the helicopter control art, each typically deals with a narrow problem and its concomitant narrow solution, such as an engine torque limitation which prevents demands on the engine in excess of the torque limit. One reference, U.S. Pat. No. 4,420,808, E. D. Diamond, et al, inventors, discloses the use of a four axis force stick and a trim controller. The 808' patent recites that it has the ability to provide the capability for a pilot to control an aircraft in response to his perception of changes in attitude, altitude, speed, heading and the like, with control inputs provided by the pilot only in the event that a change in aircraft response is required. The system of the 808' patent, then, is a trim system which sets the controls of a helicopter to their last position. This method does not take into account changing conditions such as wind shifts, or aircraft attitude. Under the system of the 808' patent, it is still the responsibility of the pilot to make the minute control changes necessary to keep the aircraft stable, or steady with respect to a fixed point on the ground. The system of the 808' patent was intended primarily to increase cockpit usable space by integrating the controls into a four axis stick with some form of control.